Directional coupler and communication unit

ABSTRACT

A directional coupler includes a main line through which a first signal in a first frequency band and a second signal in a second frequency band pass from a first port to a second port, a sub-line electromagnetically coupled to the main line and having a third port and a fourth port, the third port outputting a first coupled signal corresponding to the first signal and a second coupled signal corresponding to the second signal, a first termination circuit connected to the fourth port and used in outputting the first coupled signal, a second termination circuit connected to the fourth port and used in outputting the second coupled signal, and a first filter circuit disposed between the fourth port and the first termination circuit, wherein the first filter circuit has frequency characteristics allowing the first coupled signal to pass therethrough and attenuating the second coupled signal.

This is a continuation of U.S. patent application Ser. No. 16/139,130filed on Sep. 24, 2018 which claims priority from Japanese PatentApplication No. 2017-184015 filed on Sep. 25, 2017. The contents ofthese applications are incorporated herein by reference in theirentireties.

The present disclosure relates to a directional coupler and acommunication unit. In a mobile communication device such as a cellularphone, a directional coupler is disposed, for example, between anamplifier for a transmitted signal and an antenna. InternationalPublication No. 2016/158314, for example, discloses a directionalcoupler including a main line that serves as a transfer path for an RF(Radio-Frequency) signal, a sub-line coupled to the main line, and atermination portion including a plurality of elements and disposed atone port of the sub-line. In the disclosed directional coupler, atermination condition of the termination portion is adjusted anddirectivity of the directional coupler is improved by optionallyswitching over connections of the elements included in the terminationportion depending on a frequency of the RF signal.

Recently, a technique for transmitting and receiving RF signals in aplurality of different frequency bands at the same time in the mobilecommunication device has been developed as represented in the so-calledcarrier aggregation technology. In the directional coupler disclosed inInternational Publication No. 2016/158314, however, the followingproblem arises because the connections of the elements included in thetermination portion are switched over in accordance with turning-on/offof switches. With the configuration of the disclosed directionalcoupler, when the RF signals in the plurality of different frequencybands are supplied to the main line at the same time, the terminationcondition of a termination circuit cannot be adjusted depending on thefrequency bands of the individual RF signals, thus resulting in apossibility that the directivity may degrade.

BRIEF SUMMARY

In view of the above-described situation, the present disclosureprovides a directional coupler and a communication unit in whichdirectivity can be improved for signals in a plurality of differentfrequency bands at the same time.

According to an embodiment of the present disclosure, there is provideda directional coupler including a main line through which a first signalin a first frequency band and a second signal in a second frequency bandpass from a first port to a second port, a sub-line electromagneticallycoupled to the main line and having a third port and a fourth port, thethird port outputting a first coupled signal corresponding to the firstsignal and a second coupled signal corresponding to the second signal, afirst termination circuit connected to the fourth port and used inoutputting the first coupled signal, a second termination circuitconnected to the fourth port and used in outputting the second coupledsignal, and a first filter circuit disposed between the fourth port andthe first termination circuit, wherein the first filter circuit hasfrequency characteristics allowing the first coupled signal to passtherethrough and attenuating the second coupled signal.

According to the present disclosure, the directional coupler and thecommunication unit can be obtained in which directivity can be improvedfor the signals in the plurality of different frequency bands at thesame time.

Other features, elements, characteristics and advantages of the presentdisclosure will become more apparent from the following detaileddescription of embodiments of the present disclosure with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example of configuration of adirectional coupler according to a first embodiment of the presentdisclosure;

FIG. 2 is a block diagram illustrating an example of configuration of adirectional coupler according to a second embodiment of the presentdisclosure;

FIG. 3 is a block diagram illustrating an example of configuration of adirectional coupler according to a third embodiment of the presentdisclosure;

FIG. 4 is a block diagram illustrating an example of configuration of adirectional coupler according to a fourth embodiment of the presentdisclosure;

FIG. 5 is a graph depicting an example of simulation results of transfercharacteristics of individual paths in the directional coupler accordingto the fourth embodiment of the present disclosure;

FIG. 6A is a graph depicting an example of a simulation result ofisolation in a directional coupler according to a first comparativeexample;

FIG. 6B is a graph depicting an example of a simulation result ofdirectivity in the directional coupler according to the firstcomparative example;

FIG. 7A is a graph depicting an example of a simulation result ofisolation in the directional coupler according to the fourth embodimentof the present disclosure;

FIG. 7B is a graph depicting an example of a simulation result ofdirectivity in the directional coupler according to the fourthembodiment of the present disclosure;

FIG. 8 is a block diagram illustrating an example of configuration of adirectional coupler according to a fifth embodiment of the presentdisclosure;

FIG. 9 is a block diagram illustrating an example of configuration of adirectional coupler according to a sixth embodiment of the presentdisclosure;

FIG. 10 is a graph depicting an example of simulation results oftransfer characteristics of individual paths in the directional coupleraccording to the sixth embodiment of the present disclosure;

FIG. 11 is a block diagram illustrating an example of configuration of adirectional coupler according to a seventh embodiment of the presentdisclosure;

FIG. 12 is a graph depicting an example of simulation results oftransfer characteristics of individual paths in the directional coupleraccording to the seventh embodiment of the present disclosure;

FIG. 13 is a block diagram illustrating an example of configuration of adirectional coupler according to an eighth embodiment of the presentdisclosure;

FIG. 14 is a block diagram illustrating an example of configuration of adirectional coupler according to a ninth embodiment of the presentdisclosure;

FIG. 15 is a block diagram illustrating an example of configuration of adirectional coupler according to a tenth embodiment of the presentdisclosure;

FIG. 16A is a graph depicting an example of a simulation result of acoupling degree in a directional coupler according to a secondcomparative example;

FIG. 16B is a graph depicting an example of a simulation result of acoupling degree in the directional coupler according to the tenthembodiment of the present disclosure;

FIG. 17 is a block diagram illustrating an example of configuration of acommunication unit including the directional coupler according to thefirst embodiment of the present disclosure; and

FIG. 18 is a block diagram illustrating an example of configuration of acommunication unit including a modification of the directional coupleraccording to the first embodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described in detail belowwith reference to the drawings. It is to be noted that the same elementsare denoted by the same reference signs, and duplicate description ofthose elements is omitted.

FIG. 1 is a block diagram illustrating an example of configuration of adirectional coupler according to a first embodiment of the presentdisclosure. A directional coupler 100A illustrated in FIG. 1 is mountedon a mobile communication device such as a cellular phone and is used todetect a signal level of an RF (Radio-Frequency) signal transmitted to abase station. The directional coupler 100A is further used to distributea transmitted signal that is transmitted to the base station, and areceived signal that is received from the base station. The directionalcoupler 100A is targeted for signals according to communicationstandards such as 2G (second generation mobile communication system), 3G(third generation mobile communication system), 4G (fourth generationmobile communication system), 5G (fifth generation mobile communicationsystem), LTE (Long Term Evolution)—FDD (Frequency Division Duplex),LTE-TDD (Time Division Duplex), LTE-Advanced, and LTE-Advanced Pro, forexample. A frequency range of the RF signal is, for example, aboutseveral hundred MHz to several GHz. In addition, as described later, thedirectional coupler 100A is adaptable for the carrier aggregationtechnology and is able to couple RF signals in a plurality of differentfrequency bands and to output those RF signals at the same time. Thecommunication standards and the frequency range of the signals targetedby the directional coupler 100A are not limited to the above-mentionedones.

More specifically, the directional coupler 100A includes, for example, amain line 110, a sub-line 120, filter circuits 130 and 140, terminationcircuits 150 and 160, and ports P1 to P4.

The main line 110 is a line through which RF signals in differentfrequency bands pass from the port P1 (first port) to the port P2(second port). The RF signals may be, for example, transmitted signalsafter being amplified by a power amplifier (not illustrated) or receivedsignals having been received by an antenna. Although the frequency bandsof the RF signals supplied to the main line 110 are not limited toparticular ones, the following description is made, by way of example,on an assumption that a signal RF1 (first signal) in a frequency band(first frequency band) falling within a high band and a signal RF2(second signal) in a frequency band (second frequency band) fallingwithin a low band are supplied. The signal RF1 in the high band and thesignal RF2 in the low band may be supplied to the main line 110 at thesame time. In some cases, reflected signals of the signals RF1 and RF2may be supplied to the main line 110 in a direction toward the port P1from the port P2. The above-described combination of the frequency bandsof the signals supplied to the main line 110 is merely illustrative, andthe combined frequency bands are not limited to the high band and thelow band. In another example, signals in the high band and a middle bandmay be supplied to the main line 110 instead of the signals in the highband and the low band.

The sub-line 120 is a line electromagnetically coupled to the main line110 and constituting the coupler together with the main line 110. Thesub-line 120 has a port P3 (third port) corresponding to the port P1,and a port P4 (fourth port) corresponding to the port P2. A coupledsignal CP1 (first coupled signal) corresponding to the signal RF1 in thehigh band and a coupled signal CP2 (second coupled signal) correspondingto the signal RF2 in the low band are output from the port P3. Varioustypes of processing are carried out on the coupled signals CP1 and CP2,which have been output from the port P3, in circuits subsequent to thedirectional coupler 100A. Though not illustrated in FIG. 1, for example,a detection circuit of detecting a signal level may be disposedsubsequent to the port P3.

The filter circuit 130 (first filter circuit) is disposed between theport P4 and the termination circuit 150. The filter circuit 130 hasfrequency characteristics allowing the high-band coupled signal CP1 topass therethrough and attenuating the low-band coupled signal CP2. Onthe other hand, the filter circuit 140 (second filter circuit) isdisposed between the port P4 and the termination circuit 160. The filtercircuit 140 has frequency characteristics allowing the low-band coupledsignal CP2 to pass therethrough and attenuating the high-band coupledsignal CP1. Thus, in the directional coupler 100A, even when the signalsRF1 and RF2 in the plurality of different frequency bands are suppliedto the main line 110 at the same time, the coupled signals CP1 and CP2are distributed through the filter circuits 130 and 140 depending on thefrequency bands and are terminated by the termination circuits 150 and160, respectively.

The termination circuit 150 (first termination circuit) has apredetermined impedance value Z1 and connects the port P4 to a groundvia the filter circuit 130. The termination circuit 150 is used inoutputting the high-band coupled signal CP1. On the other hand, thetermination circuit 160 (second termination circuit) has a predeterminedimpedance value Z2 and connects the port P4 to the ground via the filtercircuit 140. The termination circuit 160 is used in outputting thelow-band coupled signal CP2.

Here, reflected signals of the leaked RF signals RF1 and RF2 are alsooutput to the port P3 in addition to the coupled signals CP1 and CP2.Moreover, the coupled signals CP1 and CP2 are reflected by the groundafter passing through the filter circuits 130 and 140 and thetermination circuits 150 and 160 from the port P4 and are then returnedto the port P4. Resulting return signals are further supplied to theport P3. Accordingly, the impedance values Z1 and Z2 of the terminationcircuits 150 and 160 can be set to values at which phases of thereflected signals leaking to the port P3 and phases of the returnsignals are opposite to each other. Hereinafter, the impedance valuessatisfying that condition are also called “proper impedance values”.When the termination circuits 150 and 160 have the proper impedancevalues, the reflected signals leaking to the port P3 are cancelled bythe return signals, and isolation (dB) is improved. Thus, directivity(dB), i.e., an index represented by a value resulting from subtracting acoupling degree from the isolation, is also improved.

The proper impedance value is different depending on the frequency ofeach signal passing through a path for the termination. In particular,because of the isolation and a band width of the frequency band being ina trade-off relation, if the signals in the plurality of differentfrequency bands share one termination circuit, degradation of theisolation becomes more significant as the frequencies of those signalsare more apart from each other.

In this embodiment, with the provision of the filter circuits 130 and140 as described above, the coupled signals CP1 and CP2 can bedistributed depending on frequencies and supplied to the paths includingthe termination circuits 150 and 160 without necessarily resorting toturning-on/off of switches. Hence the impedance values Z1 and Z2 of thetermination circuits 150 and 160 can be set to the proper impedancevalues depending on frequencies. As a result, even when the signals inthe different frequency bands are supplied to the main line 110 at thesame time as in the case of carrier aggregation, directivity of each ofthe signals in the frequency bands can be improved.

Furthermore, in this embodiment, since the directional coupler isconstituted without necessarily using any active elements, such asswitches, unlike the configuration disclosed in InternationalPublication No. 2016/158314, the manufacturing cost can be reduced.

While FIG. 1 illustrates an example in which the directional coupler100A is targeted for the signals RF1 and RF2 in two frequency bands, thenumber of frequency bands of the signals targeted by the directionalcoupler 100A may be three or more. In such a case, it is just requiredto increase the number of combinations of the filter circuits and thetermination circuits corresponding to the number of the frequency bands.

FIG. 2 is a block diagram illustrating an example of configuration of adirectional coupler according to a second embodiment of the presentdisclosure. The same elements as those in the directional coupler 100Aillustrated in FIG. 1 are denoted by the same reference signs, anddescription of those elements is omitted. Furthermore, in embodimentsdescribed below, description of matters common to those in thedirectional coupler 100A is omitted, and only different points aredescribed. In particular, similar operations and advantageous effectsobtained with similar configurations are not described in each of theembodiments.

A directional coupler 100B illustrated in FIG. 2 is different from thedirectional coupler 100A in including a multiplexer 200 instead of thefilter circuits 130 and 140.

The multiplexer 200 (first filter circuit) is disposed between the portP4 and the termination circuits 150 and 160. The multiplexer 200 hasfrequency characteristics allowing the high-band coupled signal CP1 topass therethrough and attenuating the low-band coupled signal CP2between the port P4 and the termination circuit 150. In addition, themultiplexer 200 has frequency characteristics allowing the low-bandcoupled signal CP2 to pass therethrough and attenuating the high-bandcoupled signal CP1 between the port P4 and the termination circuit 160.

With the configuration described above, the directional coupler 100B canalso provide similar advantageous effects to those obtained in thedirectional coupler 100A. A duplexer may be used instead of themultiplexer.

FIG. 3 is a block diagram illustrating an example of configuration of adirectional coupler according to a third embodiment of the presentdisclosure. A directional coupler 100C illustrated in FIG. 3 isdifferent from the directional coupler 100A illustrated in FIG. 1 in notincluding the filter circuit 140 but including termination circuits 300and 310 instead of the termination circuits 150 and 160.

The filter circuit 130 (first filter circuit) has, as described above,the frequency characteristics allowing the high-band coupled signal CP1to pass therethrough and attenuating the low-band coupled signal CP2.Accordingly, the high-band coupled signal CP1 is supplied to the path onthe side where the termination circuit 300 (first termination circuit)is disposed, but the low-band coupled signal CP2 is not supplied to thatpath. On the other hand, the high-band coupled signal CP1 and thelow-band coupled signal CP2 are both supplied to the path on the sidewhere the termination circuit 310 (second termination circuit) isdisposed.

Thus, the termination circuit 300 is used in outputting only thehigh-band coupled signal CP1. The termination circuit 310 is used inoutputting both the high-band coupled signal CP1 and the low-bandcoupled signal CP2. Accordingly, the impedance value Z4 of thetermination circuit 310 needs to be the proper impedance value for thelow-band coupled signal CP2. On the other hand, the impedance value Z3of the termination circuit 300 needs to be set such that a combinedvalue of the impedance value Z3 of the termination circuit 300 and theimpedance value Z4 of the termination circuit 310 is the properimpedance value for the high-band coupled signal CP1.

With the configuration described above, the directional coupler 100C canalso provide similar advantageous effects to those obtained in thedirectional coupler 100A. In addition, since the directional coupler100C does not include the filter circuit 140 unlike the directionalcoupler 100A, the directional coupler 100C can be constituted by asmaller number of elements.

While this embodiment has been described in connection with theconfiguration in which the directional coupler 100C includes the filtercircuit 130 allowing passage of the high band therethrough, thedirectional coupler 100C may have a configuration including, instead ofthe filter circuit 130, the filter circuit 140 allowing passage of thelow band therethrough.

FIG. 4 is a block diagram illustrating an example of configuration of adirectional coupler according to a fourth embodiment of the presentdisclosure. A directional coupler 100D illustrated in FIG. 4 representspractical examples (filter circuits 131 and 141 and termination circuits151 and 161) of the configurations of the filter circuits 130 and 140and the termination circuits 150 and 160 illustrated in FIG. 1.

The filter circuit 131 includes inductors L1 and L2 and a capacitor C1.The inductor L1 and the capacitor C1 are connected in parallel andconstitute an LC parallel resonance circuit. This LC parallel resonancecircuit is connected in series between the port P4 and the terminationcircuit 151. The constants of the inductor L1 and the capacitor C1 areset such that a resonant frequency of the above LC parallel resonancecircuit falls in the frequency band of the low band to be attenuated.With that setting, the filter circuit 131 has a very high impedance(ideally becomes open) for a low-band signal and can attenuate thelow-band coupled signal CP2. The inductor L2 is connected between anoutput of the LC parallel resonance circuit and the ground, and itfurther attenuates the low-band signal.

The filter circuit 141 includes inductors L3 and L4 and capacitors C2and C3. The inductor L3 and the capacitor C2 are connected in paralleland constitute an LC parallel resonance circuit. This LC parallelresonance circuit is connected in series between the port P4 and thetermination circuit 161. The constants of the inductor L3 and thecapacitor C2 are set such that a resonant frequency of the above LCparallel resonance circuit falls in the frequency band of the high bandto be attenuated. With that setting, the filter circuit 141 has a veryhigh impedance (ideally becomes open) for a high-band signal and canattenuate the high-band coupled signal CP1. The inductor L4 and thecapacitor C3 are connected in series and constitute an LC seriesresonance circuit. This LC series resonance circuit is connected betweenan output of the LC parallel resonance circuit and the ground, and itfurther attenuates the high-band signal. RF signals can be attenuatedover a wider band, for example, by setting a resonant frequency of theLC series resonance circuit to a higher frequency than a fundamentalwave of the high band.

The termination circuit 151 includes a resistance element R1 and acapacitor C4. The resistance element R1 and the capacitor C4 are eachconnected between an output of the filter circuit 131 and the ground.The constants of the resistance element R1 and the capacitor C4 are setsuch that a combined impedance value Z1 of the resistance element R1 andthe capacitor C4 becomes a proper value.

The termination circuit 161 includes a resistance element R2 and acapacitor C5. The resistance element R2 and the capacitor C5 are eachconnected between an output of the filter circuit 141 and the ground.The constants of the resistance element R2 and the capacitor C5 are setsuch that a combined impedance value Z2 of the resistance element R2 andthe capacitor C5 becomes a proper value.

With the configuration described above, the directional coupler 100C canalso provide similar advantageous effects to those obtained in thedirectional coupler 100A.

The above-described configurations of the filter circuits 131 and 141and the termination circuits 151 and 161 are merely examples, and thecircuit configurations are not limited to them. For instance, an LCseries resonance circuit may be used in the filter circuit 131 insteadof the inductor L2, and an inductor may be used in the filter circuit141 instead of the LC series resonance circuit. In each of thetermination circuits 151 and 161, a resonance circuit using an inductorand a capacitor, for example, may be used instead of the combination ofthe resistance element and the capacitor. In such a case, the isolationcan be further improved by setting a resonant frequency of the resonancecircuit to be matched with the frequency band of the signal to bepassed.

FIG. 5 is a graph depicting an example of simulation results of transfercharacteristics of individual paths in the directional coupler accordingto the fourth embodiment of the present disclosure. The graph depictedin FIG. 5 represents the transfer characteristics (i.e., S (Scattering)parameter S₂₁) of the individual paths including the filter circuits 131and 141 when a signal of frequencies ranging from the low band to thehigh band is supplied to the port P4 in the directional coupler 100D.Here, it is assumed that a frequency band of the supplied signalincludes a low band of about 0.6 GHz to 1 GHz, a middle band of about1.5 GHz to 2.7 GHz, and a high band of about 3.4 GHz to 3.8 GHz. In thegraph of FIG. 5, the horizontal axis indicates frequency (GHz), and thevertical axis indicates transfer characteristics (dB). In a simulationconducted here, the constants of individual elements are set such thatthe signal supplied to the port P4 is divided to flow through two paths,i.e., a path corresponding to the high band and the middle band, and apath corresponding to the low band.

As depicted in FIG. 5, in the path including the filter circuit 131, thesignal in the frequency band of the low band is greatly attenuated,while most of the signals in the frequency bands of the middle band andthe high band pass. On the other hand, in the path including the filtercircuit 141, most of the signal in the frequency band of the low bandpasses, while the signals in the frequency bands of the middle band andthe high band are greatly attenuated. It is hence understood that thefilter circuits 131 and 141 have the function of distributing thesignals.

FIG. 6A is a graph depicting an example of a simulation result ofisolation in the directional coupler according to a first comparativeexample, and FIG. 6B is a graph depicting an example of a simulationresult of directivity in the directional coupler according to the firstcomparative example. FIG. 7A is a graph depicting an example of asimulation result of isolation in the directional coupler according tothe fourth embodiment of the present disclosure, and FIG. 7B is a graphdepicting an example of a simulation result of directivity in thedirectional coupler according to the fourth embodiment of the presentdisclosure. Here, the first comparative example has a configuration inwhich, unlike the directional coupler 100D, the filter circuits 131 and141 and the termination circuits 151 and 161 are not disposed and theports P1 to P4 are each terminated through a resistance element of 50 Ω.In FIGS. 6A and 7A, the horizontal axis indicates frequency (GHz), andthe vertical axis indicates isolation (dB) (i.e., a level of thereflected signals leaking to the port P3) of the directional coupler. InFIGS. 6B and 7B, the horizontal axis indicates frequency (GHz), and thevertical axis indicates directivity (dB) (i.e., a value resulting fromsubtracting a coupling degree from the isolation) of the directionalcoupler.

As seen from FIG. 6A, in the first comparative example, the isolationdegrades down to about −40 dB particularly near 2 GHz, and a leak of thecoupled signals attributable to reflected waves is comparatively large.Moreover, as seen from FIG. 6B, the directivity remains about 20 to 25dB in the range of about 0.7 GHz to 3 GHz.

On the other hand, as seen from FIG. 7A, in the directional coupler100D, the isolation is greatly improved, i.e., about −65 dB and −55 dBnear 0.8 GHz included in the low band and near 2 GHz included in themiddle band, respectively. Moreover, as seen from FIG. 7B, correspondingto the isolation, the directivity is also greatly improved in excess ofabout 30 dB near the above-mentioned frequencies. Those results arepresumably obtained from the fact that the termination circuits 151 and161 are set to the proper impedance values in the directional coupler100D.

FIG. 8 is a block diagram illustrating an example of configuration of adirectional coupler according to a fifth embodiment of the presentdisclosure. A directional coupler 100E illustrated in FIG. 8 isdifferent from the directional coupler 100D illustrated in FIG. 4 infurther including termination circuits 152 and 162 and switch circuits400 and 410. It is to be noted that FIG. 8 illustrates only theconfiguration downstream of the port P4 in the directional coupler 100E.This point is similarly applied to FIGS. 9 and 11 described later.

In this embodiment, a high-band signal RF3 (third signal) in a frequencyband (third frequency band) different from that of the signal RF1, and alow-band signal RF4 (fourth signal) in a frequency band (fourthfrequency band) different from that of the signal RF2 are furthersupplied to the main line (not illustrated in FIG. 8). In this case, acoupled signal CP3 (third coupled signal) corresponding to the high-bandsignal RF3 and a coupled signal CP4 (fourth coupled signal)corresponding to the low-band signal RF4 are output from the port P3 inaddition to the coupled signals CP1 and CP2.

The termination circuit 152 (third termination circuit) is connected tothe port P4 and is used when the high-band coupled signal CP3 is outputfrom the port P3. An impedance value of the termination circuit 152 isset to the proper impedance value for the frequency band of the coupledsignal CP3. On the other hand, the termination circuit 162 (fourthtermination circuit) is connected to the port P4 and is used when thelow-band coupled signal CP4 is output from the port P3. An impedancevalue of the termination circuit 162 is set to the proper impedancevalue for the frequency band of the coupled signal CP4. A resistanceelement R3 and a capacitor C6 included in the termination circuit 152and a resistance element R4 and a capacitor C7 included in thetermination circuit 162 have similar configurations to those in thetermination circuits 151 and 161. Hence detailed description of thosecomponents is omitted.

The switch circuits 400 (first switch circuit) and 410 (second switchcircuit) are each an SPDT (Single-Pole Double-Throw) switch. Dependingon the frequency bands of the high-band coupled signals CP1 and CP3, theswitch circuit 400 connects the port P4 to the termination circuit 151when the coupled signal CP1 is to be output and connects the port P4 tothe termination circuit 152 when the coupled signal CP3 is to be output.Depending on the frequency bands of the low-band coupled signals CP2 andCP4, the switch circuit 410 connects the port P4 to the terminationcircuit 161 when the coupled signal CP2 is to be output and connects theport P4 to the termination circuit 162 when the coupled signal CP4 is tobe output.

With the configuration described above, the directional coupler 100E canalso provide similar advantageous effects to those obtained in thedirectional coupler 100A. In addition, because of including the switchcircuits 400 and 410, the directional coupler 100E can more finely setthe impedance values of the termination circuits 151, 152, 161 and 162than the directional coupler 100D. As a result, the directivity in eachfrequency band can be further improved.

FIG. 9 is a block diagram illustrating an example of configuration of adirectional coupler according to a sixth embodiment of the presentdisclosure. A directional coupler 100F illustrated in FIG. 9 isdifferent from the directional couplers 100A to 100E in that thedirectional coupler 100F is adaptable for a signal (third signal) in afrequency band (third frequency band) of the middle band in addition tothe high band and the low band. This embodiment is described below on anassumption that a middle-band coupled signal CP5 (third coupled signal)is output from the port P3 in addition to the high-band coupled signalCP1 and the low-band coupled signal CP2.

More specifically, the directional coupler 100F includes, for example,filter circuits 500, 510, 520, 530 and 540, and the termination circuits150, 160 and 550 downstream of the port P4. In the following,description of ones among the filter circuits 500 to 540, those oneshaving similar configurations of the filter circuits 131 and 141illustrated in FIG. 4, are omitted for the sake of simplification ofdescription while corresponding elements are denoted by the samereference signs. However, the same reference signs attached to theindividual elements do not always imply that the constants of thoseelements are the same.

The filter circuits 500 and 510 are disposed between the port P4 and thetermination circuit 150 (i.e., in a path through which the high-bandcoupled signal CP1 passes). The filter circuit 500 (first filtercircuit) includes, for example, a capacitor C8 and an inductor L5. Thecapacitor C8 is connected in series to the line interconnecting the portP4 and the termination circuit 150, and the inductor L5 is connectedbetween one output-side end of the capacitor C8 and the ground. Withsuch a configuration, the filter circuit 500 functions as a high passfilter circuit that allows the high-band signal to pass therethrough,and that attenuates the middle-band signal and the low-band signal. Thefilter circuit 510 includes, for example, an inductor L6 and a capacitorC9. The inductor L6 and the capacitor C9 are connected in parallel andconstitute an LC parallel resonance circuit. The constants of theinductor L6 and the capacitor C9 are set such that a resonant frequencyof the LC parallel resonance circuit falls in the frequency band of themiddle band to be attenuated. With that setting, the middle-band coupledsignal CP5 can be further attenuated. Thus, only the high-band coupledsignal CP1 is allowed to pass through the relevant path via the filtercircuits 500 and 510.

The filter circuits 520 and 530 are disposed between the port P4 and thetermination circuit 550 (i.e., in a path through which the middle-bandcoupled signal CP5 passes). The filter circuit 520 has a similarconfiguration to that of the filter circuit 141 illustrated in FIG. 4.The filter circuit 520 has frequency characteristics allowing themiddle-band signal and the low-band signal to pass therethrough andattenuating the high-band signal. The filter circuit 530 has a similarconfiguration to that of the filter circuit 131 illustrated in FIG. 4.The filter circuit 530 has frequency characteristics allowing thehigh-band signal and the middle-band signal to pass therethrough andattenuating the low-band signal. Thus, only the middle-band coupledsignal CP5 is allowed to pass through the relevant path via the filtercircuits 520 and 530. The filter circuit 520 and the filter circuit 530constitute one practical example of a third filter circuit incooperation with each other.

The filter circuit 540 (second filter circuit) is disposed between theport P4 and the termination circuit 160 (i.e., in a path through whichthe low-band coupled signal CP2 passes). The filter circuit 540 has asimilar configuration to that of the filter circuit 141 illustrated inFIG. 4. The filter circuit 540 has frequency characteristics allowingthe low-band signal to pass therethrough and attenuating the high-bandsignal and the middle-band signal. Thus, only the low-band coupledsignal CP2 is allowed to pass through the relevant path.

The termination circuit 550 (third termination circuit) is connected tothe port P4 and is used when the middle-band coupled signal CP5 isoutput from the port P3. In other words, an impedance value Z5 of thetermination circuit 550 is set to the proper impedance value for thefrequency band of the coupled signal CP5.

With the configuration described above, because of including the filtercircuits 500 to 540, the directional coupler 100F can distribute thecoupled signals CP1, CP2 and CP5 depending on frequencies withoutnecessarily using any switch elements and can supply those signals tothe paths including the termination circuits 150, 160 and 550,respectively. As a result, the directional coupler 100F can improve thedirectivity of each of the signals in the three frequency bands.

The order in which the filter circuit 500 and the filter circuit 510 arearranged, and the order in which the filter circuit 520 and the filtercircuit 530 are arranged are not limited to particular ones, and theymay be reversed from the illustrated orders. The above-describedconfigurations of the filter circuits 500 to 540 are merelyillustrative, and the circuit configurations are not limited to them.

FIG. 10 is a graph depicting an example of simulation results oftransfer characteristics of individual paths in the directional coupleraccording to the sixth embodiment of the present disclosure. The graphdepicted in FIG. 10 represents the transfer characteristics of theindividual paths when a signal of frequencies ranging from the low bandto the high band is supplied to the port P4 in the directional coupler100F. Here, it is assumed that a frequency band of the supplied signalincludes a low band of about 0.6 GHz to 1 GHz, a middle band of about1.5 GHz to 2.7 GHz, and a high band of about 3.4 GHz to 3.8 GHz. In thegraph of FIG. 10, the horizontal axis indicates frequency (GHz), and thevertical axis indicates transfer characteristics (dB). In a simulationconducted here, the constants of individual elements of the filtercircuits are set such that the signal supplied to the port P4 is dividedto flow through three paths corresponding to the high band, the middleband, and the low band.

As depicted in FIG. 10, in the high-band path including the filtercircuits 500 and 510, the signals in the frequency bands of the low bandand the middle band are greatly attenuated, while most of the signal inthe frequency band of the high band passes. In the middle-band pathincluding the filter circuits 520 and 530, the signals in the frequencybands of the low band and the high band are greatly attenuated, whilemost of the signal in the frequency band of the middle band passes. Inthe low-band path including the filter circuit 540, the signals in thefrequency bands of the high band and the middle band are greatlyattenuated, while most of the signal in the frequency band of the lowband passes. It is hence understood that the filter circuits 500 to 540have the function of distributing the three frequency bands.

FIG. 11 is a block diagram illustrating an example of configuration of adirectional coupler according to a seventh embodiment of the presentdisclosure. A directional coupler 100G illustrated in FIG. 11 isadaptable for signals in three frequency bands as with the directionalcoupler 100F illustrated in FIG. 9, but it has a different pathconfiguration from that of the directional coupler 100F.

More specifically, in the directional coupler 100G, the filter circuit520 connected to the port P4 attenuates the high-band signal and allowsthe signals in the middle band and the low band to pass therethrough.The signals in the middle band and the low band output from the filtercircuit 520 are further divided into the middle-band signal and thelow-band signal through the filter circuit 530 and the filter circuit540. Description of the path for the high band is omitted because it issimilar to that in the directional coupler 100F.

Thus, a method of dividing a path depending on frequency bands is notlimited to particular one. The three paths may be each directlyconnected to the port P4 as illustrated in FIG. 9, or the path may bebranched in multiple stages from the port P4 as illustrated in FIG. 11.

With the configuration described above, the directional coupler 100G canalso provide similar advantageous effects to those obtained in thedirectional coupler 100F. Moreover, in the directional coupler 100G, thelow-band signal passes through the two filter circuits 520 and 540.Accordingly, the directional coupler 100G can further attenuate, in thelow-band path, the signals in the other frequency bands withoutnecessarily increasing the number of the filter circuits in comparisonwith the directional coupler 100F.

FIG. 12 is a graph depicting an example of simulation results oftransfer characteristics of individual paths in the directional coupleraccording to the seventh embodiment of the present disclosure. The graphdepicted in FIG. 12 represents the transfer characteristics of theindividual paths, as in the graph of FIG. 10, when a signal offrequencies ranging from the low band to the high band is supplied tothe port P4 in the directional coupler 100G.

As depicted in FIG. 12, the transfer characteristics of the paths forthe high band and the middle band are not so different from thosedepicted in FIG. 10. On the other hand, in the transfer characteristicsof the path for the low band, the attenuation is larger particularly ina range of not lower than about 3GHz than that in FIG. 10. This ispresumably attributable to the fact that, as described above, thelow-band signal passes through the filter circuit 520 as well in thisembodiment. It is hence understood that the filter circuits 500 to 540have the function of distributing the three frequency bands.

FIG. 13 is a block diagram illustrating an example of configuration of adirectional coupler according to an eighth embodiment of the presentdisclosure. A directional coupler 100H illustrated in FIG. 13 isdifferent from the directional coupler 100D illustrated in FIG. 4 inthat signals are distributed depending on frequency bands through filtercircuits not only on the port P4 side, but also on the port P3 side.

More specifically, the directional coupler 100H further includes, forexample, ports P5 and P6 and the filter circuits 600 and 610.

The port P5 (first output port) is a port to which the high-band coupledsignal CP1 is output from the port P3 via the filter circuit 600. On theother hand, the port P6 (second output port) is a port to which thelow-band coupled signal CP2 is output from the port P3 via the filtercircuit 610.

The filter circuit 600 (third filter circuit) is disposed between theport P3 and the port P5. The filter circuit 600 has frequencycharacteristics allowing the high-band coupled signal CP1 to passtherethrough and attenuating the low-band coupled signal CP2. On theother hand, the filter circuit 610 (fourth filter circuit) is disposedbetween the port P3 and the port P6. The filter circuit 610 hasfrequency characteristics allowing the low-band coupled signal CP2 topass therethrough and attenuating the high-band coupled signal CP1.Because configurations of the filter circuits 600 and 610 are similar tothose of the filter circuits 131 and 141, respectively, detaileddescription of those configurations is omitted.

Thus, in the directional coupler 100H, the filter circuits 600 and 610are further disposed on the port P3 side where the coupled signals CP1and CP2 are output. As a result, the coupled signals CP1 and CP2 can bedistributed and output depending on frequency bands.

FIG. 14 is a block diagram illustrating an example of configuration of adirectional coupler according to a ninth embodiment of the presentdisclosure. A directional coupler 100I illustrated in FIG. 14 isdifferent from the directional coupler 100H illustrated in FIG. 13 inthat bidirectional signals of a traveling wave and a reflected wave bothpassing through the main line 110 can be coupled and output.

More specifically, the directional coupler 100I further includes switchcircuits 700 and 710 in comparison with the directional coupler 100H.

The switch circuit 700 (third switch circuit) and the switch circuit 710(fourth switch circuit) are each a switch for connecting each of twoinputs to either one of two outputs. More specifically, the switchcircuit 700 switches the connection destination of each of the filtercircuit 131 and the filter circuit 600 to the termination circuit 151 orthe port P5. On the other hand, the switch circuit 710 switches theconnection destination of each of the filter circuit 141 and the filtercircuit 610 to the termination circuit 161 or the port P6.

In this embodiment, the main line 110 passes the signals RF1 and RF2from the port P1 to the port P2, and simultaneously passes reflectedsignals of the signals RF1 and RF2 from the port P2 to the port P1. Thecoupled signals CP1 and CP2 of the signals RF1 and RF2 are output fromthe port P3 and coupled signals CP1 x (first reflected coupled signal)and CP2 x (second reflected coupled signal) of the reflected signals ofthe signals RF1 and RF2 are output from the port P4. Thus, thedirectional coupler 100I is able to output the bidirectional coupledsignals.

More specifically, in an operation mode (forward mode) in which thecoupled signals of the signals RF1 and RF2 are to be output, the switchcircuit 700 connects the output of the filter circuit 131 to thetermination circuit 151 and connects an output of the filter circuit 600to the port P5. The switch circuit 710 connects the output of the filtercircuit 141 to the termination circuit 161 and connects an output of thefilter circuit 610 to the port P6. Therefore, the high-band coupledsignal CP1 is output from the port P5 via the port P3, the filtercircuit 600, and the switch circuit 700. The port P4 on the terminationside is connected to the termination circuit 151 via the filter circuit131 and the switch circuit 700. In addition, the low-band coupled signalCP2 is output from the port P6 via the port P3, the filter circuit 610,and the switch circuit 710. The port P4 on the termination side isconnected to the termination circuit 161 via the filter circuit 141 andthe switch circuit 710.

On the other hand, in an operation mode (reverse mode) in which thecoupled signals of the reflected signals of the signals RF1 and RF2 areto be output, the switch circuit 700 connects the output of the filtercircuit 131 to the port P5 and connects the output of the filter circuit600 to the termination circuit 151. The switch circuit 710 connects theoutput of the filter circuit 141 to the port P6 and connects the outputof the filter circuit 610 to the termination circuit 161. Therefore, thecoupled signal CP1 x of the reflected signal in the high band is outputfrom the port P5 via the port P4, the filter circuit 131, and the switchcircuit 700. The port P3 on the termination side is connected to thetermination circuit 151 via the filter circuit 600 and the switchcircuit 700. In addition, the coupled signal CP2 x of the reflectedsignal in the low band is output from the port P6 via the port P4, thefilter circuit 141, and the switch circuit 710. The port P3 on thetermination side is connected to the termination circuit 161 via thefilter circuit 610 and the switch circuit 710.

Thus, in this embodiment, the termination circuits 151 and 161 areshared in both the forward mode and the reverse mode. Accordingly, thetermination circuit 151 is used in outputting each of the high-bandcoupled signals CP1 and CP1 x, and the termination circuit 161 is usedin outputting each of the low-band coupled signals CP2 and CP2 x.

With the configuration described above, the directional coupler 100I canalso provide similar advantageous effects to those obtained in thedirectional coupler 100H. In addition, because of including the switchcircuits 700 and 710, the directional coupler 100I is able to output thebidirectional signals.

FIG. 15 is a block diagram illustrating an example of configuration of adirectional coupler according to a tenth embodiment of the presentdisclosure. It is to be noted that FIG. 15 illustrates only theconfiguration of part of a directional coupler 100J downstream of theport P3. The directional coupler 100J illustrated in FIG. 15 isdifferent from the directional coupler 100H illustrated in FIG. 4 inthat loads are disposed in stages subsequent to the filter circuits.

More specifically, the directional coupler 100J includes, for example,filter circuits 600, 601, 610 and 611, and loads 800 and 810. In thefollowing, this embodiment is described on an assumption that thesignals in two frequency bands output from the port P3 are signals inthe middle band and the low band instead of the high band and the lowband.

The filter circuit 601 is disposed in a stage subsequent to the filtercircuit 600. The filter circuit 601 is similar to the filter circuit 600except for not including the inductor L2 among the elements of thefilter circuit 600, and it serves as a circuit for attenuating thelow-band signal in cooperation with the filter circuit 600.

The filter circuit 611 is disposed in a stage subsequent to the filtercircuit 610. The filter circuit 611 is similar to the filter circuit 610except for not including the inductor L4 and the capacitor C3 among theelements of the filter circuit 610, and it serves as a circuit forattenuating the middle-band signal in cooperation with the filtercircuit 610.

The load 800 (first load) is disposed between the filter circuit 601 andthe port P5. The load 800 includes, for example, an inductor L7 and aresistance element R5. The inductor L7 and the resistance element R5 areconnected in series in a path between the filter circuit 601 and theport P5.

The load 810 (second load) is disposed between the filter circuit 611and the port P6. The load 810 includes, for example, an inductor L8 anda resistance element R6. The inductor L8 and the resistance element R6are connected in series in a path between the filter circuit 611 and theport P6.

In this embodiment, the coupling degree between the main line 110 andthe sub-line 120 can be controlled by setting the constants of theinductors L7 and L8 and the resistance elements R5 and R6, which areincluded in the loads 800 and 810, thus adjusting impedances of theloads 800 and 810 depending on frequency bands. More specifically, theimpedances of the loads 800 and 810 are adjusted such that a deviationof the coupling degree depending on frequencies is reduced. As a result,when the directional coupler 100J is used to detect RF signals, adeviation between signal levels of the coupled signals is reduced andaccuracy in the detection can be improved.

The port P5 and the port P6 may be connected to each other such that thesignals in the middle band and the low band may be output from oneoutput port.

FIG. 16A is a graph depicting an example of a simulation result of acoupling degree in a directional coupler according to a secondcomparative example, and FIG. 16B is a graph depicting an example of asimulation result of a coupling degree in the directional coupleraccording to the tenth embodiment of the present disclosure. Here, thesecond comparative example has a configuration in which, unlike thedirectional coupler 100J illustrated in FIG. 15, the filter circuits600, 601, 610 and 611 and the loads 800 and 810 are not disposed and thecoupled signals are directly output from the port P3. In the graphs ofFIGS. 16A and 16B, the horizontal axis indicates frequency (GHz), andthe vertical axis indicates coupling degree (dB) between the port P1 andthe port P3 (i.e., between the output ports to which the port P5 and theport P6 are connected in the directional coupler 100J).

As depicted in FIG. 16A, in the second comparative example, the couplingdegree has characteristics represented by a curve moderately curvingdepending on frequencies. In the frequency range of about 0.8 GHz to 2.8GHz, for example, the coupling degree varies within a width from about−27 dB to −22 dB.

On the other hand, as depicted in FIG. 16B, in the directional coupler100J, an average coupling degree is lower than that in the secondcomparative example, but it has substantially horizontalcharacteristics. It is seen that the coupling degree in the frequencyrange of about 0.8 GHz to 2.8 GHz is about −34 dB to −32 dB, and thatthe coupling degree varies in a smaller width than that in the secondcomparative example. Thus, the directional coupler 100J is able tosuppress the deviation between levels of the coupled signals to beoutput.

FIG. 17 is a block diagram illustrating an example of configuration of acommunication unit including the directional coupler according to thefirst embodiment of the present disclosure. A communication unit 1000Aillustrated in FIG. 17 represents an example of configuration in whichdistribution of a transmitted signal and a received signal in a cellularphone, for example, is implemented using the directional coupler 100A.

More specifically, the communication unit 1000A includes, for example,an RFIC 1100, a power amplifier (PA) 1200, a low noise amplifier (LNA)1300, and the directional coupler 100A.

The RFIC 1100 is a circuit for executing, for example, production of atransmitted signal Tx that is to be transmitted from an antenna (notillustrated), and processing of received signals Rx that has beenreceived by the antenna.

The power amplifier 1200 amplifies the power of the transmitted signalTx, which has been produced in the RFIC 1100, to a level necessary fortransmission, and then outputs the transmitted signal Tx. Thetransmitted signal Tx is supplied to the antenna from the port P2 in thedirectional coupler 100A via the port P1.

The low noise amplifier 1300 amplifies the power of each of the receivedsignals Rx (including first received signal and second received signal)in a plurality of frequency bands, which have been received by theantenna, and then outputs the received signals Rx to the RFIC 1100.

In this embodiment, the directional coupler 100A is used to supply thereceived signals Rx to the low noise amplifier 1300. More specifically,in the main line 110, the received signals Rx are supplied to the portPb, and the transmitted signal Tx is supplied to the port P2. Moreover,coupled signals of the received signals Rx are output from the port P3.Here, the port P4 is connected, as described above, to the terminationcircuits 150 and 160 in a way distributed through the filter circuits130 and 140 depending on frequency bands. Although a coupled signal ofthe transmitted signal Tx is output from the port P4, the coupled signalof the transmitted signal Tx flows to the ground via the terminationcircuits 150 and 160. In other words, the termination circuits 150 and160 function as the termination circuits in outputting the coupledsignals of the received signals Rx, and further has the function ofcausing the coupled signal of the transmitted signal Tx to flow to theground.

With the communication unit 1000A having the above-describedconfiguration, when the transmitted signal Tx and the received signalsRx are supplied to one main line 110, only signals corresponding to thereceived signals Rx can be taken out. Thus, the received signals can betaken out without necessarily using a duplexer or a circulator, forexample.

Furthermore, since this embodiment includes combinations of the filtercircuits 130 and 140 and the termination circuits 150 and 160 in aone-to-one relation to the frequency bands, it is possible to achievehigh isolation among the plurality of frequency bands, and to suppressleakage of the transmitted signal to the reception path. As a result,the communication unit 1000A can realize high reception accuracy whensignals in the same frequency band are transmitted and received at thesame time.

The termination circuits 150 and 160 may be adjusted to have the properimpedance values for frequencies in different frequency bands.Alternatively, one termination circuit 150 may be adjusted to have theproper impedance values for a frequency of the transmitted signal in apredetermined frequency band, and the other termination circuit 160 maybe adjusted to have the proper impedance values for a frequency of thereceived signal in the predetermined frequency band. With thecombinations of the filter circuits and the termination circuits thatare adjusted to have the proper impedance values for the respectivefrequencies of the transmitted signal and the received signal asdescribed above, a pass band of each filter circuit can be set to acomparatively narrow band, and high isolation can be realized.

The directional coupler applied to the communication unit 1000A is notlimited to the directional coupler 100A, and suitable one of thedirectional couplers according to the other various embodiments is alsoapplicable. For example, the directional coupler 100H illustrated inFIG. 13 may be applied instead of the directional coupler 100A. In sucha case, the communication unit includes two low noise amplifiers, andthe ports P5 and P6 illustrated in FIG. 13 are connected to those twolow noise amplifiers in a one-to-one relation. As a result, signals indifferent frequency bands can be received at the same time.

FIG. 18 is a block diagram illustrating an example of configuration of acommunication unit including a modification of the directional coupleraccording to the first embodiment of the present disclosure. Acommunication unit 1000B illustrated in FIG. 18 represents an example ofconfiguration in which distribution of the transmitted signal and thereceived signal is implemented, as in the communication unit 1000Aillustrated in FIG. 17, using a directional coupler 100A′ that is amodification of the directional coupler 100A.

More specifically, the communication unit 1000B is different from thecommunication unit 1000A in further including an analog cancellationcircuit 1400 and an adder 1500. Moreover, the communication unit 1000Bincludes the directional coupler 100A′ substituted for the directionalcoupler 100A.

In the directional coupler 100A′, unlike the directional coupler 100A,respective outputs of the termination circuits 150 and 160 are connectedto the analog cancellation circuit 1400 instead of being connected tothe ground.

The coupled signal of the transmitted signal Tx is individually suppliedto the analog cancellation circuit 1400 from the port P4 via the filtercircuits 130 and 140 and the termination circuits 150 and 160. Then, theanalog cancellation circuit 1400 produces, from the supplied signal, asignal having a phase that is opposite, when compared in the adder 1500,to a phase of the transmitted signal included in a signal supplied fromthe port P3 and supplies the produced signal to the adder 1500.

The adder 1500 adds the coupled signal (including a component of thetransmitted signal Tx) of each received signal Rx, which is suppliedfrom the port P3, and the signal output from the analog cancellationcircuit 1400, and outputs a resulting signal to the low noise amplifier1300.

In other words, the coupled signal of each received signal Rx outputfrom the port P3 includes the transmitted signal Tx leaking to the portP3 side. In this embodiment, the component of the transmitted signal Txleaking to the port P3 side and the signal produced by the analogcancellation circuit 1400 and having the phase opposite to that of thetransmitted signal Tx cancel each other in the adder 1500. Thus, thecomponent of the transmitted signal Tx included in the coupled signal ofthe received signal Rx can be removed.

With the configuration described above, the communication unit 1000B canremove the component of the transmitted signal Tx leaking to thereception circuit by utilizing the coupled signal of the transmittedsignal Tx, which is output from the port P4. Accordingly, thecommunication unit 1000B can provide higher reception accuracy than thecommunication unit 1000A.

The RFIC 1100 may include a digital cancellation circuit 1600, asillustrated in FIG. 18, such that the component of the transmittedsignal included in the received signal after being amplified is furthercanceled through digital processing carried out by the digitalcancellation circuit 1600.

Furthermore, in FIG. 18, respective outputs of the termination circuits150 and 160 may be combined into one output and supplied to the analogcancellation circuit 1400 instead of supplying the coupled signal of thetransmitted signal through separated paths from the termination circuits150 and 160 to the analog cancellation circuit 1400.

The analog cancellation circuit 1400 may control a level of thetransmitted signal supplied to the adder 1500 to become substantiallythe same as that of the transmitted signal included in the receivedsignal supplied to the adder 1500 from the port P3, and then may supplythe controlled signal to the adder 1500.

The exemplary embodiments of the present disclosure have been describedabove. Each of the directional couplers 100A (100A′) to 100I includesthe main line 110 through which the signals RF1 and RF2 pass from theport P1 to the port P2, the sub-line 120 electromagnetically coupled tothe main line 110 and having the port P3 and the port P4, the port P3outputting the coupled signal CP1 corresponding to the signal RF1 andthe coupled signal CP2 corresponding to the signal RF2, the terminationcircuit 150 connected to the port P4 and used in outputting the coupledsignal CP1, the termination circuit 160 connected to the port P4 andused in outputting the coupled signal CP2, and the filter circuit 130disposed between the port P4 and the termination circuit 150, whereinthe filter circuit 130 has the frequency characteristics allowing thecoupled signal CP1 to pass therethrough and attenuating the coupledsignal CP2. Hence the coupled signals CP1 and CP2 can be distributeddepending on frequencies without necessarily resorting to turning-on/offof switches. Accordingly, the impedance values Z1 and Z2 of thetermination circuits 150 and 160 can be set to the proper impedancevalues depending on frequencies. As a result, even when the signals inthe plurality of different frequency bands are supplied to the main line110 at the same time, the directivity of each of the signals in theplurality of frequency bands can be improved.

Each of the directional couplers 100A (100A′) and 100D to 100J furtherincludes the filter circuit 140 disposed between the port P4 and thetermination circuit 160 and having the frequency characteristicsallowing the coupled signal CP2 to pass therethrough and attenuating thecoupled signal CP1. Hence the coupled signals CP1 and CP2 can bedistributed depending on frequencies. As a result, the directivity ofeach of the signals in the plurality of frequency bands can be improved.

Furthermore, in each of the directional couplers 100D, 100E, and 100H to100J, the filter circuit 131 includes the LC parallel resonance circuithaving the resonant frequency that falls within the frequency band ofthe low band, and the filter circuit 141 includes the LC parallelresonance circuit having the resonant frequency that falls within thefrequency band of the high band. Accordingly, since the filter circuits131 and 141 have very high impedances for the signals in the low bandand the high band, respectively, the coupled signals CP2 and CP1 in thelow band and the high band can be attenuated.

The directional coupler 100E further includes the termination circuits152 and 162 each connected to the port P4, and the switch circuits 400and 410. The main line 110 passes the signals RF3 and RF4 in the otherdifferent frequency bands therethrough from the port P1 to the port P2,and the sub-line 120 further outputs the coupled signal CP3corresponding to the signal RF3 and the coupled signal CP4 correspondingto the signal RF4 from the port P3. The switch circuit 400 supplies thecoupled signal CP1 to the termination circuit 151 and the coupled signalCP3 to the termination circuit 152, and the switch circuit 410 suppliesthe coupled signal CP2 to the termination circuit 161 and the coupledsignal CP4 to the termination circuit 162. The termination circuit 152is used in outputting the coupled signal CP3, and the terminationcircuit 162 is used in outputting the coupled signal CP4. Accordingly,the directional coupler 100E can more finely set the impedance values ofthe termination circuits 151, 152, 161 and 162 than the directionalcoupler 100D. As a result, the directivity in each frequency band can befurther improved in the directional coupler 100E.

Each of the directional couplers 100F and 100G further includes thetermination circuit 550 connected to the port P4, and the filtercircuits 520 and 530 both disposed between the port P4 and thetermination circuit 550. The main line 110 passes the signal RF5 in theother different frequency band therethrough from the port P1 to the portP2, and the sub-line 120 further outputs the coupled signal CP5corresponding to the signal in the relevant frequency band from the portP3. The filter circuits 500 and 510 have the frequency characteristicsallowing the coupled signal CP1 to pass therethrough and attenuating thecoupled signals CP2 and CP5 in cooperation with each other, the filtercircuit 540 has the frequency characteristics allowing the coupledsignal CP2 to pass therethrough and attenuating the coupled signals CP1and CP5, and the filter circuits 520 and 530 have the frequencycharacteristics allowing the coupled signal CP5 to pass therethrough andattenuating the coupled signals CP1 and CP2 in cooperation with eachother. Hence the coupled signals CP1, CP2 and CP5 can be distributeddepending on frequencies without necessarily resorting to turning-on/offof switches. According to the directional couplers 100F and 100G,therefore, the directivity of the signal in each of three frequencybands can be further improved.

Each of the directional couplers 100H to 100J further includes the portP5 from which the coupled signal CP1 is output, the port P6 from whichthe coupled signal CP2 is output, the filter circuit 600 disposedbetween the port P3 and the port P5 and having the frequencycharacteristics allowing the coupled signal CP1 to pass therethrough andattenuating the coupled signal CP2, and the filter circuit 610 disposedbetween the port P3 and the port P6 and having the frequencycharacteristics allowing the coupled signal CP2 to pass therethrough andattenuating the coupled signal CP1. Hence the coupled signals CP1 andCP2 can be distributed depending on frequency bands and then output.

The directional coupler 100J further includes the load 800 disposedbetween the filter circuit 600 and the port P5, and the load 810disposed between the filter circuit 610 and the port P6, wherein thecoupling degree between the main line 110 and the sub-line 120 isadjusted by the load 800 and the load 810. Hence a deviation of thecoupling degree depending on frequencies can be reduced. As a result,when the directional coupler 100J is used to detect RF signals, accuracyin the detection can be improved.

The directional coupler 100I further includes the switch circuit 700switching the connection destination of each of the filter circuit 131and the filter circuit 600 to the termination circuit 151 or the portP5, and the switch circuit 710 switching the connection destination ofeach of the filter circuit 141 and the filter circuit 610 to thetermination circuit 161 or the port P6. The port P4 outputs the coupledsignal CP1 x corresponding to the reflected signal of the signal RF1 andthe coupled signal CP2 x corresponding to the reflected signal of thesignal RF2. As a result, the directional coupler 100I is able to outputbidirectional signals of a traveling wave and a reflected wave.

In the directional coupler 100C, the filter circuit 140 is not disposed,and the termination circuit 310 is used in outputting both the coupledsignals CP1 and CP2. As a result, the directional coupler 100C can beconstituted using a smaller number of elements than that used in thedirectional coupler 100A.

Each of the communication unit 1000A and 1000B includes the directionalcoupler 100A or 100A′ and the low noise amplifier 1300. Each of thesignal RF1 and the signal RF2 contains the received signal Rx havingbeen received by the antenna, and the coupled signals CP1 and CP2 areboth supplied to the low noise amplifier 1300. Thus, when thetransmitted signal Tx and the received signals Rx are supplied to onemain line 110, signals corresponding to the received signals Rx can beoutput from the port P3. According to the communication units 1000A and1000B, therefore, the received signal can be taken out withoutnecessarily using a duplexer or a circulator. In addition, since acombination of the filter circuit and the termination circuit isdisposed for each frequency band, high isolation can be achieved amongthe plurality of frequency bands. As a result, high reception accuracycan be realized when signals in the same frequency band are transmittedand received at the same time.

It is to be noted that the above-described embodiments are merelyillustrative with intent to make easier understanding of the presentdisclosure, and they should not be construed as limiting the presentdisclosure. The present disclosure can be modified and/or improvedwithout departing from the gist of the disclosure, and the presentdisclosure includes equivalents to the matters disclosed in the presentdisclosure as well. In other words, modifications resulting fromchanging designs of the embodiments as appropriate by those skilled inthe art are also included in the scope of the present disclosure insofaras having the features of the present disclosure. For instance,individual constituent elements in the embodiments, and layouts,materials, conditions, shapes, sizes, etc. of those constituent elementsare not limited to the illustrated ones, and they may be changed asappropriate. In addition, the constituent elements in the embodimentsmay be combined with each other insofar as being technically feasibleand resulting combinations of the constituent elements are also includedin the scope of the present disclosure insofar as having the features ofthe present disclosure.

While embodiments of the disclosure have been described above, it is tobe understood that variations and modifications will be apparent tothose skilled in the art without departing from the scope and spirit ofthe disclosure. The scope of the disclosure, therefore, is to bedetermined solely by the following claims.

1. A directional coupler comprising: a first port and a second port; amain line connecting the first port to the second port and which isconfigured to pass a first signal in a first frequency band and a secondsignal in a second frequency band pass; a third port and a fourth port,the third port being configured to output a first coupled signalcorresponding to the first signal and to output a second coupled signalcorresponding to the second signal; a first termination circuitconnected to the fourth port; a second termination circuit connected tothe fourth port; and a first filter circuit disposed between the fourthport and the first termination circuit, wherein the first filter circuithas a pass band corresponding to a frequency of the first coupled signaland an attenuation band corresponding to a frequency of the secondcoupled signal.
 2. The directional coupler according to claim 1, furthercomprising a second filter circuit disposed between the fourth port andthe second termination circuit, wherein the second filter circuit has apass band corresponding to the frequency of the second coupled signaland an attenuation band corresponding to the frequency of the firstcoupled signal.
 3. The directional coupler according to claim 2,wherein: the first filter circuit comprises a band-rejection filtercircuit having a resonant frequency that falls within the secondfrequency band, and the second filter circuit comprises a band-rejectionfilter circuit having a resonant frequency that falls within the firstfrequency band.
 4. The directional coupler according to claim 2, furthercomprising: a third termination circuit and a fourth terminationcircuit, the third and fourth termination circuits each connected to thefourth port; and a first switch circuit and a second switch circuit,wherein: the main line is further configured to pass a third signal in athird frequency band and a fourth signal in a fourth frequency band, thethird port is further configured to output a third coupled signalcorresponding to the third signal and to output a fourth coupled signalcorresponding to the fourth signal, the first switch circuit isconfigured to selectively supply the first coupled signal to the firsttermination circuit and the third coupled signal to the thirdtermination circuit, and the second switch circuit is configured toselectively supply the second coupled signal to the second terminationcircuit and the fourth coupled signal to the fourth termination circuit.5. The directional coupler according to claim 4, wherein the firstswitch is disposed between the first filter circuit and the first andthird termination circuits, and the second switch is disposed betweenthe second filter circuit and the second and fourth terminationcircuits.
 6. The directional coupler according to claim 2, furthercomprising: a third termination circuit connected to the fourth port;and a third filter circuit disposed between the fourth port and thethird termination circuit, wherein: the main line is further configuredto pass a third signal in a third frequency band, the third port isfurther configured to output a third coupled signal corresponding to thethird signal from the third port, the attenuation band of the firstfilter circuit further corresponds to a frequency of the third coupledsignal, the attenuation band of the second filter circuit furthercorresponds to the frequency of the third coupled signal, and the thirdfilter circuit has a pass band corresponding to the frequency of thethird coupled signal and an attenuation band corresponding to thefrequencies of the first coupled signal and the second coupled signal.7. The directional coupler according to claim 2, further comprising: afirst output port configured to output the first coupled signal; asecond output port configured to output the second coupled signal; athird filter circuit disposed between the third port and the firstoutput port, and having a pass band corresponding to the frequency ofthe first coupled signal and an attenuation band corresponding to thefrequency of the second coupled signal; and a fourth filter circuitdisposed between the third port and the second output port, and having apass band corresponding to the frequency of the second coupled signaland an attenuation band corresponding to the frequency of the firstcoupled signal.
 8. The directional coupler according to claim 7, furthercomprising: a first load disposed between the third filter circuit andthe first output port; and a second load disposed between the fourthfilter circuit and the second output port.
 9. The directional coupleraccording to claim 7, further comprising: a third switch circuitconfigured to selectively connect each of the first filter circuit andthe third filter circuit to the first termination circuit or the firstoutput port; and a fourth switch circuit configured to selectivelyconnect each of the second filter circuit and the fourth filter circuitto the second termination circuit or the second output port, wherein:the fourth port is configured to output a first reflected coupled signalcorresponding to a reflected signal of the first signal and to output asecond reflected coupled signal corresponding to a reflected signal ofthe second signal, when the directional coupler is configured to outputthe first coupled signal or the second coupled signal, the third switchcircuit connects an output of the first filter circuit to the firsttermination circuit and an output of the third filter circuit to thefirst output port, and the fourth switch circuit connects an output ofthe second filter circuit to the second termination circuit and anoutput of the fourth filter circuit to the second output port, and whenthe directional coupler is configured to output the first reflectedcoupled signal or the second reflected coupled signal, the third switchcircuit connects the output of the first filter circuit to the firstoutput port and the output of the third filter circuit to the firsttermination circuit, and the fourth switch circuit connects the outputof the second filter circuit to the second output port and the output ofthe fourth filter circuit to the second termination circuit.
 10. Thedirectional coupler according to claim 1, wherein the first filtercircuit is a multiplexer.
 11. The directional coupler according to claim1, wherein the frequency of the first coupled signal is greater than thefrequency of the second coupled signal.
 12. A communication unitcomprising: the directional coupler according to claim 1; and a lownoise amplifier, wherein: the first signal and the second signal arereceived by an antenna, and the low noise amplifier is configured toreceive the first coupled signal and the second coupled signal.
 13. Thedirectional coupler according to claim 3, further comprising: a thirdtermination circuit and a fourth termination circuit, the third andfourth termination circuits each connected to the fourth port; and afirst switch circuit and a second switch circuit, wherein: the main lineis further configured to pass a third signal in a third frequency bandand a fourth signal in a fourth frequency band, the third port isfurther configured to output a third coupled signal corresponding to thethird signal and to output a fourth coupled signal corresponding to thefourth signal, the first switch circuit is configured to selectivelysupply the first coupled signal to the first termination circuit and thethird coupled signal to the third termination circuit, and the secondswitch circuit is configured to selectively supply the second coupledsignal to the second termination circuit and the fourth coupled signalto the fourth termination circuit.
 14. The directional coupler accordingto claim 3, further comprising: a first output port configured to outputthe first coupled signal; a second output port configured to output thesecond coupled signal; a third filter circuit disposed between the thirdport and the first output port, and having a pass band corresponding tothe frequency of the first coupled signal and an attenuation bandcorresponding to the frequency of the second coupled signal; and afourth filter circuit disposed between the third port and the secondoutput port, and having a pass band corresponding to the frequency ofthe second coupled signal and an attenuation band corresponding to thefrequency of the first coupled signal.
 15. The directional coupleraccording to claim 4, further comprising: a first output port configuredto output the first coupled signal; a second output port configured tooutput the second coupled signal; a third filter circuit disposedbetween the third port and the first output port, and having a pass bandcorresponding to the frequency of the first coupled signal and anattenuation band corresponding to the frequency of the second coupledsignal; and a fourth filter circuit disposed between the third port andthe second output port, and having a pass band corresponding to thefrequency of the second coupled signal and an attenuation bandcorresponding to the frequency of the first coupled signal.
 16. Acommunication unit comprising: the directional coupler according toclaim 2; and a low noise amplifier, wherein: the first signal and thesecond signal are received by an antenna, and the low noise amplifier isconfigured to receive the first coupled signal and the second coupledsignal.
 17. A communication unit comprising: the directional coupleraccording to claim 3; and a low noise amplifier, wherein: the firstsignal and the second signal are received by an antenna, and the lownoise amplifier is configured to receive the first coupled signal andthe second coupled signal.
 18. A communication unit comprising: thedirectional coupler according to claim 4; and a low noise amplifier,wherein: the first signal and the second signal are received by anantenna, and the low noise amplifier is configured to receive the firstcoupled signal and the second coupled signal.